This invention relates to chlorinated low unsaturation rubbers having both improved adhesion properties and also improved covulcanizability with high unsaturation rubbers and a method for making same.
Chlorobutyl rubber possesses many desirable properties such as exceptionally good air impermeability, flex properties and especially good heat resistance and aging properties. The commercial success of chlorobutyl rubber is largely dependent on its application in such things as tire innerliners and sidewalls, conveyor or power transmission belting, steam hoses, wire insulation, etc. Chlorobutyl rubber has proved to be useful in applications inaccessible to butyl rubber owing to the fact that the chlorinated sites of chlorobutyl enhance covulcanization of chlorobutyl with high unsaturation rubbers. Even with this improved covulcanization, it has long been recognized that the degree of covulcanization of chlorobutyl with high unsaturation rubber was not complete enough to allow for the use of chlorobutyl with high unsaturation rubber in all of the applications where its desirable properties would be advantageous. The properties which had to be improved before chlorobutyl could be effectively covulcanized with certain high unsaturation rubber for such uses as high performance tire innerliners and sidewalls were (1) the adhesion of chlorobutyl vulcanizates to high unsaturation rubber vulcanizates, and (2) improved tensile strength and dynamic stability of covulcanizates of chlorobutyl with high unsaturation rubber.
It has long been known in the art that the adhesion of chlorobutyl to high unsaturation rubber could be improved by the addition of small amounts of bromobutyl rubber to chlorobutyl rubber. Such a technique is disclosed in U.S. Pat. No. 2,992,670, wherein a minor proportion of bromobutyl is blended with a major proportion of chlorobutyl in order to improve the adhesion properties of chlorobutyl with high unsaturation rubber.
Another technique for improving the adhesion properties of chlorobutyl with high unsaturation rubber is disclosed in U.S. Pat. No. 2,933,117, which teaches that a chlorinated butyl inner lining of a tubeless tire can be adhered to a carcass containing one or more high unsaturation rubbers by the introduction of an interposed layer containing an admixture of a high unsaturation rubber and a brominated butyl rubber.
Still another technique for adhering chlorobutyl to a high unsaturation rubber is disclosed in U.S. Pat. No. 2,975,816, wherein a laminated rubber structure was prepared which consisted of:
1. AN INNER LINING OF CHLOROBUTYL AND A HIGH UNSATURATION RUBBER MODIFIED WITH CERTAIN N-bromo compounds;
2. A CARCASS LAYER CONTAINING ONE OR MORE HIGH UNSATURATION RUBBERS MODIFIED WITH A N-bromo compound, and
3. AN OUTER RUBBER LAYER CONTAINING AT LEAST ONE RUBBER POLYMER.